The benzimidazole fungicides are used throughout the world under several brand names, including Benoyml and lignasan. These compounds can control a variety of fungal pathogens on vegetables, fruits and trees, including grey mould (Botrytis cinerea Pers.), powdery mildews (Erisyphe, Sphaerotheca), Dutch Elm Disease (Ceratocystis ulmi), brown rot (Monilinia fructicola) etc. Unfortunately, the fungidical effectiveness of the benzimidazoles has been significantly reduced due to the development of resistant fungal strains. The cause of this resistance has been attributed to a lack of penetration of the benzimidazoles through the outer fungal membranes (See Gessler, Phytopath. Z., 85: 35-38 (1976)).
A combination of benzimidazole fungicides and surfactants is known in the art, for example, U.S. Pat. No. 3,930,010 to H. L. Klopping teaches that the fungicidal activity of the benzimidazole compound is improved by combination with a surfactant at or above its critical micelle concentration (CMC).
Accordingly an object of the present invention is to provide a fungicidal composition containing as the main ingredient a fungicidal benzimidazole compound, the activity of which is increased by the addition of a synergist.
Another object of the present invention is to provide a method of combatting fungi employing a fungicidal benzimidazole compound, the effectiveness of which is enhanced by the addition of a synergist against fungi including benzimidazole-susceptible as well as benzimidazole-tolerant or -resistant fungi.
Still another object of the present invention is to provide a method for restoring or recovering the fungidical activity of the benzimidazole fungicide against benzimidazole-tolerant or -resistant fungi.
These and other objects of the present invention will be apparent to the person skilled in the art from the subsequent detailed description of the invention.
It has now been found that the mixture of benzimidazoles with alkyl pyridinium salts provides a unique combination that eliminates the fungal resistance factor and substantially improved the effectiveness of the fungicidal activity of the benzimidazole compounds, even at a concentration of the alkyl pyridinium salts far below its critical micelle concentration (CMC) level.